From: Robert Schrader (rms@cts.com)
Date: Wed Mar 12 1997 - 18:59:22 MST
On Thu, 13 Mar 1997, Mitchell Porter wrote:
> I've recently been thinking about time-reversal symmetry in physics.
> {snip}
> If time-reversal symmetry is real, it ought to be possible to have
> beings like ourselves whose "arrow of time" points the other way.
>
> Is there something paradoxical about the notion of *communication*
> between ourselves and countertime beings? Or could we build a
> time-reversed robot that reports on the future?
> {snip}
> In the case of countertime communication I see no such convenient
> physical mechanism to avoid paradoxes of the form: at time t,
> countertime machine A tells "forward-time" machine B that B sent a
> signal at time t+dt, and B is programmed not to send the signal if
> it receives such a message from A. So perhaps countertime entities
> aren't possible, or communication with them is not possible, but
> if so, why not?
It seems that if you can even recognize that another being ( or another
universe? ) is reversed in time to yourself, you have enough information
transfer to be able to communicate sufficiently to trigger the above
paradox.
Therefore, either 1) we can't even know of their existence, or 2) we have
a paradox. Separate universes?
Hmm...maybe a third possibility is one-way communication, but that
argues against symmetry...I'm in over my head here.
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